Effect of Porous Surface Layer on Leaching Rate of Radionuclide from Cementitious Waste Form.

Leach tests based on IAEA methods were carried out using three types of cementitious specimens containing 134 Cs and 125 ! and an evaluation method of apparent diffusion coefficients from the leaching curves was discussed.Since the gradient of the leaching curve, i.e. the relationship between the leaching ratio and the square root of time, changes during the leach tests, it has been difficult to estimate the diffusion coefficient.The difference between the leaching rate in the early period of the leach test and that in the later period was attributed to the porous microstructure of the surface layer in the cementitious specimens.The duplicate layer model, which expressed differences in the properties between the surface layer and an inner region by different diffusion coefficients, was proposed.Its numerical solutions had good agreement with the experimental leaching curves.